The objective of this research is to investigate a recently discovered mechanism contributing to the regulation of photosynthetic carbon metabolism in plants. Specific aims address the regulation of a chloroplast enzyme, 2-carboxyarabinitol 1-phosphatase (CA 1-Pase). Ca 1-Pase participates as a component of the multiple mechanisms regulating the primary carbon fixing enzyme, ribulose 1,5 bisphosphate carboxylase/oxygenase (Rubisco). Understanding this complex system poses a unique problem in cellular biochemistry. Long term goals seek to elucidate and characterize key metabolic control points in carbon fixation (e.g. Rubisco), and to reduce existing limitations to plant productivity. This is basic research whose health related mission is general: to enhance production of food, and plant-related pharmaceutical products. The proposal will use standard biochemical techniques and assays to investigate regulation of CA 1-Pase which catalyses the degradation of 2-carboxyarabinitol-1-phosphate (CA 1-P), a tight-binding inhibitor of Rubisco. CA 1-P is a phosphate ester synthesized in leaves in response to darkness or reduced light intensity. Experiments will investigate the response of purified CA 1-Pase to positive and negative effectors, and also its likely interaction with the ferredoxin/thioredoxin system. Light regulation of CA 1-Pase, and the consequent reversal of inhibition of Rubisco will also be addressed at the cellular level using isolated leaf protoplasts and chloroplasts.